28-06-2012, 11:14 AM
Resonant Conversion
[attachment=25865]
Introduction to Resonant Conversion
Resonant power converters contain resonant L-C networks whose
voltage and current waveforms vary sinusoidally during one or more
subintervals of each switching period. These sinusoidal variations are
large in magnitude, and the small ripple approximation does not apply.
Some types of resonant converters:
• Dc-to-high-frequency-ac inverters
• Resonant dc-dc converters
• Resonant inverters or rectifiers producing line-frequency ac
Resonant conversion: advantages
The chief advantage of resonant converters: reduced switching loss
Zero-current switching
Zero-voltage switching
Turn-on or turn-off transitions of semiconductor devices can occur at
zero crossings of tank voltage or current waveforms, thereby reducing
or eliminating some of the switching loss mechanisms. Hence
resonant converters can operate at higher switching frequencies than
comparable PWM converters
Zero-voltage switching also reduces converter-generated EMI
Zero-current switching can be used to commutate SCRs
In specialized applications, resonant networks may be unavoidable
High voltage converters: significant transformer leakage
inductance and winding capacitance leads to resonant network
Resonant conversion: disadvantages
Can optimize performance at one operating point, but not with wide
range of input voltage and load power variations
Significant currents may circulate through the tank elements, even
when the load is disconnected, leading to poor efficiency at light load
Quasi-sinusoidal waveforms exhibit higher peak values than
equivalent rectangular waveforms
These considerations lead to increased conduction losses, which can
offset the reduction in switching loss
Resonant converters are usually controlled by variation of switching
frequency. In some schemes, the range of switching frequencies can
be very large
Complexity of analysis
Resonant conversion: Outline of discussion
• Simple steady-state analysis via sinusoidal approximation
• Simple and exact results for the series and parallel resonant
converters
• Mechanisms of soft switching
• Circulating currents, and the dependence (or lack thereof) of
conduction loss on load power
• Quasi-resonant converter topologies
• Steady-state analysis of quasi-resonant converters
• Ac modeling of quasi-resonant converters via averaged switch
modeling
[attachment=25865]
Introduction to Resonant Conversion
Resonant power converters contain resonant L-C networks whose
voltage and current waveforms vary sinusoidally during one or more
subintervals of each switching period. These sinusoidal variations are
large in magnitude, and the small ripple approximation does not apply.
Some types of resonant converters:
• Dc-to-high-frequency-ac inverters
• Resonant dc-dc converters
• Resonant inverters or rectifiers producing line-frequency ac
Resonant conversion: advantages
The chief advantage of resonant converters: reduced switching loss
Zero-current switching
Zero-voltage switching
Turn-on or turn-off transitions of semiconductor devices can occur at
zero crossings of tank voltage or current waveforms, thereby reducing
or eliminating some of the switching loss mechanisms. Hence
resonant converters can operate at higher switching frequencies than
comparable PWM converters
Zero-voltage switching also reduces converter-generated EMI
Zero-current switching can be used to commutate SCRs
In specialized applications, resonant networks may be unavoidable
High voltage converters: significant transformer leakage
inductance and winding capacitance leads to resonant network
Resonant conversion: disadvantages
Can optimize performance at one operating point, but not with wide
range of input voltage and load power variations
Significant currents may circulate through the tank elements, even
when the load is disconnected, leading to poor efficiency at light load
Quasi-sinusoidal waveforms exhibit higher peak values than
equivalent rectangular waveforms
These considerations lead to increased conduction losses, which can
offset the reduction in switching loss
Resonant converters are usually controlled by variation of switching
frequency. In some schemes, the range of switching frequencies can
be very large
Complexity of analysis
Resonant conversion: Outline of discussion
• Simple steady-state analysis via sinusoidal approximation
• Simple and exact results for the series and parallel resonant
converters
• Mechanisms of soft switching
• Circulating currents, and the dependence (or lack thereof) of
conduction loss on load power
• Quasi-resonant converter topologies
• Steady-state analysis of quasi-resonant converters
• Ac modeling of quasi-resonant converters via averaged switch
modeling